Diffuse characterized histone substitution levels and By profilying the epigenome of H3K27M mutant DIPG patient cells I found that H3K27M co-localizes with H3K27 acetylation (H3K27ac). In accordance with previous biochemical data, heterotypic H3K27M- K27ac nucleosomes co-localize with bromodomain proteins at actively transcribed genes, whereas PRC2 is excluded from these regions, suggesting that PRC2 is not sequestered at sites of incorporation of H3K27M. I also showed that the heterotypic nucleosomes H3K27M-K27ac co- localize with bromodomain proteins in DIPG, importantly treatment with BET bromodomain inhibitors in DIPG xenograft mouse models potently reduces tumor growth and extend animal survival. During my mentored phase (K99) I'm planning to study the molecular details of the formation of the heterotypic nucleosomes using in vitro biochemistry and molecular biology assays and gather further insights in the pathogenic mechanisms of aberrant acetylation and H3K27M deposition in DIPG. While transitioning toward the independent phase (R00) I'm planning to improve the BET inhibitors therapeutic strategy by identifying mechanisms of resistance and cooperative factors that can lead to an improved and durable therapy for children affected by DIPG. Altogether my plan is to perform experiments that push forward our knowledge of this incurable disease with the goal of finally having a standard-of-care option that can offer a reliable and efficacious treatment for DIPG patients. Intrinsic Glioma (DIP G) a highly aggressive pediatric brainstem tumor by rapid and nearly uniform patient demise. A heterozygous point mutation of H3 occurs in more than 80% of these tumors, and results in a lysine-to-methionine (H3K27M). Expression of this histone mutant is accompanied by a reduction in the of Polycomb Repressive Complex 2 (PRC2) mediated H3K27 trimethylation (H3K27me3) this is hypothesized to be a driving event of DIPG oncogenesis. Pontine is